WDPN32 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) WARNING NR 
036//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (ATSANI), LOCATED APPROXIMATELY 191 NM 
SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED WEST-NORTHWESTWARD AT 02 
KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL 
SATELLITE IMAGERY (MSI) REVEALS A FULLY-EXPOSED LOW LEVEL 
CIRCULATION CENTER (LLCC) WITH TIGHTLY-CURVED BANDING WRAPPING INTO 
THE CENTER. FURTHERMORE, THE MSI INDICATES THAT THE SYSTEM HAS 
DEGRADED, SHOWING ONLY SHORT BURSTS OF DEEP CONVECTION OVER THE 
NORTHEAST QUADRANT, RAPIDLY BEING SHEARED TO THE NORTHEAST UNDER 
MODERATE (20-25 KT) VERTICAL WIND SHEAR (VWS). BASED ON THE FULLY-
EXPOSED LLCC IN MSI AND A WELL-DEFINED LLCC IN A 070530Z AMSR2 89 
GHZ MICROWAVE IMAGE, THERE IS GOOD CONFIDENCE IN THE INITIAL 
POSITION. THE INITIAL INTENSITY IS ASSESSED AT 40 KTS AND IS HEDGED 
SLIGHTLY HIGHER THAN MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES 
OF T2.5 (35 KTS, PGTW/RJTD) BASED ON A 070528Z AMSR2 WINDSPEED 
ESTIMATE REVEALING AN AREA WITH 40 KT WINDS TO THE NORTH. IN 
CONJUNCTION WITH THE AFOREMENTIONED MODERATE VWS, ENVIRONMENTAL 
ANALYSIS REVEALS MARGINALLY WARM (25-26 CELSIUS) SEA SURFACE 
TEMPERATURES (SST) AND ENHANCED POLEWARD OUTFLOW, CONTRIBUTING TO AN 
OVERALL MARGINAL ENVIRONMENT. TS 23W IS SLOWLY TRACKING ALONG THE 
SOUTHWESTERN PERIPHERY OF A WEAK SUBTROPICAL RIDGE (STR) POSITIONED 
TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 23W IS EXPECTED TO TURN SHARPLY SOUTHWESTWARD AFTER TAU 06 
AS LOW-LEVEL RIDGING ASSOCIATED WITH A NORTHEAST SURGE EVENT 
STRENGTHENS OVER THE EAST CHINA SEA. TS 23W IS FORECAST TO 
ACCELERATE ALONG THIS TRACK AS IT STEADILY WEAKENS DUE TO INCREASING 
(30+ KTS) VWS AND COOLER SST VALUES (24-26 CELSIUS). THE SYSTEM IS 
EXPECTED TO DISSIPATE OVER WATER BY TAU 36, IF NOT SOONER, AS THE 
ENVIRONMENT QUICKLY DEGRADES. OVER THE PAST SIX HOURS, NUMERICAL 
MODEL GUIDANCE HAS SIGNIFICANTLY CHANGED, WITH SEVERAL MODELS LOSING 
THE VORTEX SIGNATURE WITHIN THE POOR ENVIRONMENT AND OTHER MODEL 
SOLUTIONS LOSING THE VORTEX SIGNATURE IN THE NEXT 12 HOURS. HOWEVER, 
THE JTWC TRACK HAS MAINTAINED A 36 HOUR FORECAST TO ACCOUNT FOR THE 
TIME NEEDED FOR THE SYSTEM TO WEAKEN. BASED ON THE MODEL CHANGE AND 
GENERALLY UNFAVORABLE ENVIRONMENT, THERE IS LOW CONFIDENCE IN THE 
JTWC FORECAST TRACK.//
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